+
+bool PHIElimination::SplitPHIEdges(MachineFunction &MF,
+ MachineBasicBlock &MBB,
+ LiveVariables &LV,
+ MachineLoopInfo *MLI) {
+ if (MBB.empty() || !MBB.front().isPHI() || MBB.isLandingPad())
+ return false; // Quick exit for basic blocks without PHIs.
+
+ bool Changed = false;
+ for (MachineBasicBlock::const_iterator BBI = MBB.begin(), BBE = MBB.end();
+ BBI != BBE && BBI->isPHI(); ++BBI) {
+ for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2) {
+ unsigned Reg = BBI->getOperand(i).getReg();
+ MachineBasicBlock *PreMBB = BBI->getOperand(i+1).getMBB();
+ // We break edges when registers are live out from the predecessor block
+ // (not considering PHI nodes). If the register is live in to this block
+ // anyway, we would gain nothing from splitting.
+ // Avoid splitting backedges of loops. It would introduce small
+ // out-of-line blocks into the loop which is very bad for code placement.
+ if (PreMBB != &MBB &&
+ !LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB)) {
+ if (!MLI ||
+ !(MLI->getLoopFor(PreMBB) == MLI->getLoopFor(&MBB) &&
+ MLI->isLoopHeader(&MBB))) {
+ if (PreMBB->SplitCriticalEdge(&MBB, this)) {
+ Changed = true;
+ ++NumCriticalEdgesSplit;
+ }
+ }
+ }
+ }
+ }
+ return Changed;
+}